First "date" advice: beers after work. Good advice besides being myself?

Well, i have an online dating profile (like almost anyone these days) and tonight i have a "date" something more like a get together, beers after work, with this guy i've been talking for more than 3 weeks. Seems enough!

So we get along well, he seems like a nice person and everything. The only thing is that i don't know if i'm really his type... i'm more the books type and he is more the outdoorsy type. But on the chat we seem to hit it off!

I've been out on a couple dates and some have turned out on second dates... but others which i think went great didn't turned out on a second... so what am i doing wrong? how to know if its a really good date?

I don't talk about my ex boyfriends, i offer to split, i'm am nice (or so i've been told), i dress up but not too much, i'm not loud and i don't think i'm awfully boring... so, ideas?